The last Texas Democrat to run simultaneously for the U.S. Senate and vice president won both races - and later became the first Texan in the White House.

But Lyndon Johnson's dual 1960 victories cost his party a Senate seat they have yet to win back.Under the state law custom-written for Johnson in 1959, Sen. Lloyd Bentsen of Texas could pursue similar dual candidacies this year. Bentsen, long a powerful vote-getter and money-raiser on the Texas ballot, is among the potential running mates under consideration by expected Democratic presidential nominee Michael Dukakis.

Bentsen is a heavy favorite to win re-election to the Senate over Republican challenger Beau Boulter, a West Texas congressman, in November. But if Bentsen became vice president, his Senate seat would be declared open in January, and Texas Gov. Bill Clements, a Republican, would appoint an interim replacement.

A full-time replacement would be picked by the voters in a spring special election, the same route Republican John Tower used in 1961 to replace Johnson in a wild race that drew 70 candidates.

Tower and Bill Blakley, a Democrat appointed as interim senator by then-Democratic Gov. John Connally, advanced to a runoff, which Tower won.

The Democrats could never beat Tower. He retired in 1984, and Republican Phil Gramm won the seat.

Texas Democrats eager to see Bentsen on the national ticket say they do not fear a recurrence of the GOP's big win in 1961.

"We're confident that if the Democratic ticket wins and Sen. Bentsen is vice president, there is going to be an attitude and mood in this state that would facilitate electing a Democrat to replace Sen. Bentsen," said Ed Martin, executive director of the Texas Democratic Party.

It would be, however, a junior Democratic senator whose clout would be far less than that now wielded by Bentsen as Senate Finance Committee chairman.

Texas Democratic Chairman Bob Slagle said the possibility of losing the Senate seat is "always a matter of concern."

"But that doesn't cause me to wish Sen. Bentsen was not on the ticket" with Dukakis, he said.

Mark Sanders, spokesman for the Republican Party of Texas, said the GOP "could pick up" Bentsen's seat in a special election, but it would be a tough battle. Running for both jobs, though legal in Texas, is not fair, he said.

"Lloyd Bentsen needs to decide what he wants to be," Sanders said. "I don't think it's the right thing to do for someone to run for two offices, especially important offices like this. You can't play games like that with Texas voters."

Boulter, Bentsen's senate race opponent, said it would be "greedy" for Bentsen to run for two jobs.

"He's making it look like the Senate is unimportant," Boulter said.